Longwall mining involves the removal of coal from a single longwall face, generally 80-200 m in length. The coal is extracted by a cutter, for example, a rotary drum shearer that is attached to the front of the longwall conveyor frame and runs on a flexible segmented rail typically referred to as the face conveyor track. The face conveyor track extends along the length of the working area. The extracted coal is passed on to a flexible conveyor located immediately behind the face conveyor track. The coal is then conveyed to a transfer point located in one of the access headings, for example, the headgate at the side of the longwall panel.
The mine roof along the working area is protected by moveable hydraulic roof supports, such as shields, chocks, or other supports. As more coal is extracted, these roof supports are moved forward. The roof supports are typically located behind the pan line of the longwall conveyor frame and are attached to, but can be moved independently of, the longwall conveyor frame. The roof behind the line is allowed to collapse as the line moves forward. The longwall conveyor frame is advanced by hydraulic cylinders located adjacent the roof support structures behind the pan line. When the cutter has completed a pass, the roof supports are advanced independently of the longwall conveyor frame. Once the roof supports have been advanced the required distance, the longwall conveyor frame is then advanced so that at no time is the face conveyor track exposed to an unsupported roof.
After a complete block of coal is mined, it is necessary to disassemble the longwall conveyor frame, including the roof supports, and move the equipment to a new face. Because the roof supports extend out over the conveyor, there is insufficient space to disassemble and remove the roof supports if they are located too close to the longwall face. Therefore, the roof supports are typically not advanced during the last few passes of the cutter into the longwall face. Advancing the cutter and conveyor without advancing the roof supports; however, leaves an unsupported roof area at the longwall face.
Some conditions require the roof to be supported; therefore, the roof must be bolted after each pass of the cutter to avoid collapse. Typically, stopers are used to manually drill bolt holes in the mine roof along the longwall face after the roof supports stop advancing. Because the roof supports are not advanced, the stoper operators must install temporary supports and are unprotected from falling roof material during such installation.
Although hydraulic roof bolting machines are known, such machines are extremely bulky and heavy and require a great deal of space for maneuvering and installation along a longwall face. Such machines are acceptable where there is plenty of space for maneuvering large equipment. However, in situations where space is limited such prior roof bolting machines are impractical. In order to install such large roof bolting machines it would be necessary to shut down and disassemble either the headgate or tailgate drive after each cut, attach the roof bolting machine to the face conveyor track, reassemble the headgate or tailgate drive, and then make an additional cut. This procedure is very time consuming and labor intensive.